The Mental Health Foundation (MHF) says up to 20% of children suffer some form of mental problem, while 10% need professional help.

It is calling for a wide-ranging debate about society's values and priorities which it says are putting increasing pressures on children.

The MHF's figures are higher than other estimates. Government statistics suggest that between seven and 10% of youngsters suffer from anorexia or depression.

The MHF claims studies show that anxiety disorders and those which cause disruptive behaviour, affect round 10% of those aged between four and 20.

Substance abuse can affect around 6%.

The study is the work of an MHF committee which looked at 1,200 pieces of evidence from parents, young people, teachers and social workers.

It was part of a �1m three-year programme, which is said to be the most comprehensive study this century into the mental health of children and teenagers.

June McKerrow, director of the Mental Health Foundation, said that, although some of the illnesses included in the report were temporary and mild, research suggested that if they were not properly dealt with they could develop into something worse.

She said children needed more help to become more "emotionally literate" so they could speak about their problems.

But she did not think the report's results were surprising given that one in five adults are thought to suffer from a mental illness at any given time.

"Growing up is difficult and painful and we live in a pressurised society," she said.

"The problems are getting worse. We are obsessed by material rewards, economic pressures and physical safety which all influence mental health," she stated, adding that life for children had become "more regimented".

Time and space

She added that family fragmentation, pressure at school, a lack of space and time to develop skills and abilities and parents' growing concerns about letting their children play outside were partly to blame for the problem.